1. Field of the Invention
The present invention generally relates to a bandwidth controlling method and a node apparatus station for a ring-based network.
2. Description of the Related Art
FIG. 1 shows an exemplary configuration of a ring-based network in which RPR (Resilient Packet Ring) is applied over a SONET (Synchronous Optical Network). In FIG. 1, by providing SONET path in two directions between each of the adjacently disposed node apparatuses (RPR stations) 1A-1D, all of the the node apparatuses 1A-1D can be connected by a pair of bidirectional SONET paths of equal bandwidth. An RPR ring is provided over this SONET path.
A technology for managing/controlling the bandwidth and flow of an RPR network is disclosed in Japanese Laid-Open Patent Application NO. 2004-289799.
With these kinds of ring-based networks, there is a demand to increase/decrease the physical bandwidth without having to affect the traffic (paths being in use). Nevertheless, such ring-based networks have the following disadvantages.
First, in a case of changing the ring bandwidth of the RPR network (RPR over SONET) from an upper level NMS (Network Management System), it is necessary for the SONET path to be removed in order to reset the bandwidth. This causes a state of signal disconnection for a maximum period of approximately 30 minutes (although this may vary depending on the number of nodes in the network).
Second, although the changing of a SONET path between a pair of adjacent nodes (i.e. changing of a single span) may be performed in a short period of time, the RPR requires the bandwidth for all spans in the ring network to be changed simultaneously since any inconsistency in bandwidth among the spans may cause an abnormality in the performance of the RPR. Therefore, the bandwidth of the ring cannot be changed with an RPR application.
Furthermore, in a case where a failure occurs in the SONET path, an RPR protection function switches the RPR regardless of whether the error has little influence with respect to a bandwidth guarantee service. This leads to a problem of inefficient use of bandwidth.